Analytical analysis
Independent samples T-test used for comparing the frequency of different factors between unipolar non-steroid-eluting and bipolar steroid-eluting leads. Logistic regression was used in the case of categorical variables with more than two categories. Survival analysis was done on a subgroup of patients, that their lead failure was due to the primary failure reasons (unacceptable high pacing threshold and sensing abnormality, lead fracture, loss of capture, and lead displacement). The characteristics of these patients were also calculated and presented with the abovementioned descriptive analysis. For a 48-month follow-up time, Kaplan Meier analysis and Weibull regression hazards model was used for survival analysis of all variables.9Accordingly, hazard ratio was estimated for each variable with a 95% confidence interval (95%CI). Afterward, age and lead type (bipolar steroid-eluting and unipolar non-steroid eluting) adjusted hazard ratio calculated for variables using Weibull regression hazards model. The level of significance was considered as p<0.05 throughout the study.